Output Regulation Circuit of a Power Converter without Current Sensing Loss and Method Thereof

ABSTRACT

An output regulation circuit of a power converter without current sensing loss includes a transforming circuit to receive a proportional voltage from the primary winding of the power converter. The first proportional voltage is transformed to a charging current signal. When the power switch during on-time period, the charging current signal charges an energy storage device. Thus, the circuit controls the power switch according to a voltage limited signal of the energy storage device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an output regulation circuit and morespecifically relates to an output regulation circuit of a powerconverter without current sensing loss.

2. Description of Related Art

Resistor-based current sensing is simple, easy to use, low-cost,extremely linear, and requires no calibration. Ohm's Law states thatvoltage across a resistor is directly proportional to the currentthrough it: V=IR. As a caveat, however, note that all resistorsdissipate power when current passes though them. Because the dissipationproduces heat that, in turn, affects the resistance, power dissipationin a sensing resistor must be carefully assessed.

FIG. 1 shows a conventional current sensing circuit of the powerconverter. A sensing resistor 12 is coupled to the power switch 11 ofthe power converter 10. In continuous conduction mode operation, whenthe power switch 11 enables, the input voltage excites the transformer13. Hence, the input current I_(p) is increased, and transforms to avoltage signal V_(ref) by the sensing resistor 12. The comparator 141 ofthe control IC 14 receives the voltage signal V_(ref) to compare with afeedback signal V_(feb). When the current reaches the predeterminedvalue, the power switch 11 disables. Until the next period, the powerswitch 11 will enable to output energy steady.

Due to the sensing resistor 12 exists in the main power loop, the powerdissipation in the sensing resistor 12 is depends on the current. Thecurrent is greater, and the loss will increase. Therefore, a need existsfor a lossless method to sense current.

SUMMARY OF THE INVENTION

An objective of the invention is to provide an output regulation circuitof a power converter without current sensing loss.

In accordance with the invention, an output regulation circuit isprovided. The output regulation circuit includes a first transformingcircuit and an energy storage device. The first transforming circuitreceives a first proportional voltage from a primary winding of a powerconverter when the power switch during on time period. And the firsttransforming circuit transforms the first proportional voltage to acharging current signal. Then when the power switch during on-timeperiod the charging current signal charges the energy storage device toproduce a voltage limited signal, which is proportional to the switchcurrent of the power switch, to control the power switch of the powerconverter.

Furthermore, the output regulation circuit further includes a secondtransforming circuit. The second transforming circuit receives a secondproportional voltage from a auxiliary winding of the power converterwhen the power switch during off time period, and transforms the secondproportional voltage to a discharging current signal. Then when thepower switch during off-time period the energy storage device isdischarged by the discharging current signal, and produces the voltagelimited signal, which is proportional to output voltage of the secondarywinding of the power converter, to control the power switch.

Thus, the output regulation circuit of the invention would control thepower switch of the power converter without loss. Also, without thesensing resistor of the conventional power converter, the powerconverter is more stable in the large power. Moreover, the inventionalso provides a method for output regulation of a power converter. Themethod comprises a step of obtaining a charging current signal, beingproportional to an input voltage of the power converter, when the powerswitch of the power converter during on time period, a step of chargingan energy storage device by the charging current signal when the powerswitch of the power converter during on-time period, and a step ofcontrolling the power switch of the power converter according to avoltage limited signal of the energy storage device.

Furthermore, the method of the present invention further comprises astep of obtaining a discharging current signal, being proportional to anoutput voltage of the power converter, when the power switch of thepower converter during off time period, a step of discharging the energystorage device by the discharging current signal when the power switchof the power converter during off-time period, and a step of controllingthe power switch of the power converter according to the voltage limitedsignal of the energy storage device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below illustration only, and thus arenot limitative of the present invention, and wherein:

FIG. 1 shows a conventional current sensing circuit of the powerconverter.

FIG. 2 is an output regulation circuit of the power converter accordingto present invention.

FIG. 3 shows the first and second transforming circuit in the FIG. 2.

FIG. 4 displays the waveform of the present invention in continuousconduction mode operation.

FIG. 5 displays the waveform of the present invention in discontinuousconduction mode operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a preferred embodiment of an output regulation circuit ofthe power converter according to present invention. The power converter20 includes a primary winding 21, a secondary winding 22, an auxiliarywinding 23, a power switch 24, a control circuit 25 and an energystorage device 26. The primary winding 21 receives an input voltageV_(IN) and is coupled to the secondary winding 22 to induce signals inthe secondary winding 22 and outputs an output voltage V_(O). Theprimary winding 21 also connects to the power switch 24. The controlcircuit 25 connects to the primary winding 21 and the power switch 24 tocontrol the power converter 20 by turn-on/turn-off the power switch 24.The primary winding 21 and the secondary winding 22 is inversely. Whenthe power switch 24 during on-time period, the current of the primarywinding 21 is defined as follows:

$\begin{matrix}{I_{L\text{-}{on}} = {\frac{V_{IN}}{L} \times T_{on}}} & (1)\end{matrix}$

wherein T_(on) is time of the power switch 24 power converter 20 duringon-time period; and

-   -   L is inductance of the primary winding 21.

The auxiliary winding 23 and the secondary winding 22 is not inversely.When the power switch 24 during off-time period, the reflected currentof the auxiliary winding 23 is defined as follows:

$\begin{matrix}{I_{L\text{-}{off}} = {n \times \frac{V_{bus}}{L} \times T_{off}}} & (2)\end{matrix}$

wherein T_(on) is time of the power switch 24 power converter 20 duringoff-time period;

-   -   L is inductance of the primary winding 21; and    -   n is turns ratio between primary and secondary winding.

The control circuit 25 includes a first transforming circuit 251, asecond transforming circuit 252, an oscillation circuit 253(OSC), aflip-flop 254 and, a comparator 255 and two stitches 256, 257. The OSC253 is connected to the clock-input terminal CK of a flip-flop 254. Theauxiliary winding 23 is connected to the D-input terminal D of theflip-flop 254. The reset-input terminal R of the flip-flop 254 isconnected to the output terminal of the comparator 255. The outputterminal Q of the flip-flop 254 is connected to the power switch 24 andthe first transforming circuit 251 switch 256. Another output terminal Qof the flip-flop 254 is connected to the second transforming circuit 252switch 257.

The first transforming circuit 251 obtains a first proportional voltageV₁, which is proportional to the input voltage V_(IN) of the powerconverter 20, during on time period. As FIG. 2 shown, the firstproportional voltage V₁ is divided from the input voltage V_(IN) byresistors R_(C) and R_(D). However we can also obtain the firstproportional voltage V₁ from any place of the power converter 20 tosatisfy the first proportional voltage V₁ is proportional to the inputvoltage V_(IN). Even the power converter 20 further includes a signalgenerator to generate the first proportional voltage V₁ is proper. Toavoid increase the cost, the embodiment discloses obtaining the firstproportional voltage V₁ is divided from the input voltage V_(IN) by theresistors R_(C) and R_(D), which included in conventional powerconverter 20.

Then the first transforming circuit 251 transforms the firstproportional voltage V₁ to a charging current signal. When the powerswitch 24 is during on-time period the flip-flop 254 sends a controlsignal S₁ through output terminal Q to turn on the switch 256 and thecharging current signal charges the energy storage device 26 during ontime period. The energy storage device 26 can be an electric capacity,an inductance or any other device can store energy. The energy storagedevice 26 would produce a voltage limited signal V_(L) to the comparator255 and compares with a reference voltage V_(R) to control the powerswitch 24 of the power converter 20.

The second transforming circuit 252 obtains a second proportionalvoltage V₂, which is proportional to the output voltage V_(O) of thepower converter 20, during off time period. As FIG. 2 shown, the secondproportional voltage V₂ is divided from the reflected output voltage,which is proportional to the output voltage V_(O), by resistors R_(A)and R_(B). However we can also obtain the second proportional voltage V₂from any place of the power converter 20 to satisfy the secondproportional voltage V₂ is proportional to the output voltage V_(O).Even the power converter 20 further includes a signal generator togenerate the second proportional voltage V₂ is proper. To avoid increasethe cost, the embodiment discloses obtaining the second proportionalvoltage V₂ is divided from the reflected output voltage by the resistorsR_(A) and R_(B), which included in conventional power converter 20.

Then the second transforming circuit 252 transforms the secondproportional voltage V₂ to a discharging current signal. When the powerswitch 24 is during off-time period the flip-flop 254 sends a controlsignal S2 through output terminal Q to turn on the switch 257 and thedischarging current signal discharges the energy storage device 26during off time period. The energy storage device 26 produces thevoltage limited signal V_(L) to the comparator 255 and compares with areference voltage V_(R) to control the power switch 24 of the powerconverter 20.

FIG. 3 shows the first and second transforming circuit in the FIG. 2.The first transforming circuit 251 includes a first voltage-currentconverter 31 and a first current mirror circuit 32. The firstvoltage-current converter 31 transforms the first proportional voltageV₁ to a first current I₁. The first current mirror circuit 32 mirrorsthe first current I₁ to the charging current signal SC and charges theenergy storage device 26. The voltage limited signal V_(L) of the energystorage device 26 when the power switch 24 during on-time period isaccording to following equation:

$\begin{matrix}{V_{L\text{-}{on}} = {x \times \frac{V_{IN} \times A}{C} \times \frac{T_{on}}{R_{x}}}} & (3)\end{matrix}$

wherein x is current mirror transfer ratio;

-   -   C is capacitance of the energy storage device 26;    -   V_(IN) is the input voltage of the power converter 20;    -   A is the proportion of the first proportional voltage V₁;    -   T_(on) is time of the power switch 24 power converter 20 during        on-time period; and    -   R_(x) is a voltage to current conversion ration.

In the embodiment of FIG. 2, the proportion A of the first proportionalvoltage V₁ is

$\frac{R_{C}}{R_{C} + R_{D}}.$

Comparing equations 1 and 3, the voltage limited signal V_(L) in theenergy storage device 26 is proportional to a switch current of thepower switch 24. Hence, we can take the voltage limited signal V_(L) inthe energy storage device 26 to replace the switch current of the powerswitch 24 during on-time period. And the voltage limited signal V_(L) istransmitted to the comparator 255 to control the power switch 24 duringon-time period.

The second transforming circuit 252 includes a second voltage-currentconverter 33 and two second current mirror circuits 34, 35. The secondvoltage-current converter 33 transforms the second proportional voltageV₂ to a second current I₂. The second current mirror circuits 34, 35mirror the second current I₂ to the discharging current signal S_(D) anddischarges the energy storage device 26. The voltage limited signalV_(L) of the energy storage device 26 when the power switch 24 duringoff-time period is according to following equation:

$\begin{matrix}{V_{L\text{-}{off}} = {y \times \frac{V_{O} \times B}{C} \times \frac{T_{off}}{R_{y}} \times N_{x}}} & (4)\end{matrix}$

wherein y is current mirror transfer ratio;

-   -   C is capacitance of the energy storage device 26;    -   V_(O) is the output voltage of the power converter 20;    -   B is the proportion of the second proportional voltage V₂;    -   T_(off) is time of the power switch 24 power converter 20 during        off-time period;    -   N_(x) is a turns ratio of the auxiliary winding 23 and the        secondary winding 22; and    -   R_(y) is a voltage to current conversion ration.

In the embodiment of FIG. 2, the proportion B of the first proportionalvoltage V₂ is

$\frac{R_{A}}{R_{A} + R_{B}}.$

Comparing equations 2 and 4, the voltage limited signal V_(L) in theenergy storage device 26 is proportional to a switch current of thepower switch 24. Hence, we can take the voltage limited signal V_(L) inthe energy storage device 26 to replace the switch current of the powerswitch 24 during off-time period. And the voltage limited signal V_(L)is transmitted to the comparator 255 to control the power switch 24during off-time period.

FIG. 4 displays the waveform of the present invention in continuousconduction mode operation. And FIG. 5 displays the waveform of thepresent invention in discontinuous conduction mode operation. Regardlessof in continuous conduction mode operation or in discontinuousconduction mode operation, we can control the power switch by thevoltage limited signal V_(L) of the energy storage device 26 by chargingand discharging.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A method for output regulation of a power converter, the powerconverter including a power switch, comprising the following steps:obtaining a charging current signal, being proportional to an inputvoltage of the power converter; charging an energy storage device by thecharging current signal, when the power switch of the power converterduring on-time period; and controlling the power switch of the powerconverter according to a voltage limited signal of the energy storagedevice.
 2. The method of claim 1, wherein the step of obtaining thecharging current signal further comprise the following steps: obtaininga first proportional voltage being proportional to the input voltage ofthe power converter; transforming the first proportional voltage to afirst current; and mirroring the first current to the charging currentsignal.
 3. The method of claim 2, wherein the first proportional voltageis obtained from the input voltage of the power converter.
 4. The methodof claim 3, wherein the voltage limited signal of the energy storagedevice when the power switch during on-time period is according tofollowing equation:$V_{L\text{-}{on}} = {x \times \frac{V_{IN} \times A}{C} \times \frac{T_{on}}{R_{x}}}$wherein x is current mirror transfer ratio; C is capacitance of theenergy storage device; V_(IN) is an input voltage of the powerconverter; A is the proportion of the first proportional voltage; T_(on)is time of the power switch during on-time period; and Rx is a voltageto current conversion ration.
 5. The method of claim 1, wherein thevoltage limited signal in the energy storage device is proportional to aswitch current of the power switch.
 6. The method of claim 1, furthercomprising the steps of: obtaining a discharging current signal, beingproportional to an output voltage of the power converter; dischargingthe energy storage device by the discharging current signal, when thepower switch of the power converter during off-time period; andcontrolling the power switch of the power converter according to thevoltage limited signal of the energy storage device.
 7. The method ofclaim 6, wherein the step of obtaining the discharging current signalfurther comprise the following steps: obtaining a second proportionalvoltage being proportional to the output voltage of the power converter;transforming the second proportional voltage to a second current; andmirroring the second current to the discharging current signal.
 8. Themethod of claim 7, wherein the second proportional voltage is obtainedfrom the output voltage of the power converter.
 9. The method of claim6, wherein the voltage limited signal of energy storage device when thepower switch during off-time period is according to following equation:$V_{L\text{-}{off}} = {y \times \frac{V_{O} \times B}{C} \times \frac{T_{off}}{R_{y}} \times N_{x}}$wherein y is current mirror transfer ratio; C is capacitance of theenergy storage device; V_(O) is an output voltage of the powerconverter; B is the proportion of the second proportional voltage;T_(off) is time of the power switch during off-time period; Nx is aturns ratio of the auxiliary winding and the secondary winding; andR_(y) is a voltage to current conversion ration.
 10. The method of claim6, wherein the voltage limited signal in the energy storage device isproportional to the output voltage of the power converter.
 11. A methodfor output regulation of a power converter, the power converterincluding a power switch, comprising the following steps: obtaining adischarging current signal, being proportional to an output voltage ofthe power converter; discharging the energy storage device by thedischarging current signal, when the power switch of the power converterduring off-time period; and controlling the power switch of the powerconverter according to the voltage limited signal of the energy storagedevice.
 12. The method of claim 11, wherein the step of obtaining thedischarging current signal further comprise the following steps:obtaining a second proportional voltage being proportional to the outputvoltage of the power converter; transforming the second proportionalvoltage to a second current; and mirroring the second current to thedischarging current signal.
 13. The method of claim 12, wherein thevoltage limited signal of energy storage device when the power switchduring off-time period is according to following equation:$V_{L\text{-}{off}} = {y \times \frac{V_{O} \times B}{C} \times \frac{T_{off}}{R_{y}} \times N_{x}}$wherein y is current mirror transfer ratio; C is capacitance of theenergy storage device; V_(O) is an output voltage of the powerconverter; B is the proportion of the second proportional voltage;T_(off) is time of the power switch during off-time period; Nx is aturns ratio of the auxiliary winding and the secondary winding; andR_(y) is a voltage to current conversion ration.
 14. The method of claim12, wherein the second proportional voltage is obtained from the outputvoltage of the power converter.
 15. A output regulation circuit of apower converter, the power converter including a primary winding, asecondary winding, an auxiliary winding and a power switch, comprising:a first transforming circuit, receiving a first proportional voltagefrom the primary winding of the power converter, and transforming thefirst proportional voltage to a charging current signal; and an energystorage device, charged by the charging current signal when the powerswitch during on-time period; wherein the energy storage device producesa voltage limited signal, which is proportional to switch current of thepower switch, to control the power switch of the power converter. 16.The circuit of claim 15, wherein the first transforming circuitcomprises: a first voltage-current converter, transforming the firstproportional voltage to a first current; and a first current mirrorcircuit, mirroring the first current to the charging current signalbefore charging the energy storage device.
 17. The circuit of claim 16,the voltage limited signal of the energy storage device when the powerswitch during on-time period is according to following equation:$V_{L\text{-}{on}} = {x \times \frac{V_{IN} \times A}{C} \times \frac{T_{on}}{R_{x}}}$wherein x is current mirror transfer ratio; C is capacitance of theenergy storage device; V_(bus) is an input voltage of the powerconverter; A is the proportion of the first proportional voltage; T_(on)is time of the power switch during on-time period; and Rx is a voltageto current conversion ration.
 18. The circuit of claim 15, wherein theenergy storage device is an electric capacity.
 19. The circuit of claim15, wherein the energy storage device is an inductance.
 20. The circuitof claim 15, further comprising: a second transforming circuit,receiving a second proportional voltage from the auxiliary winding ofthe power converter, and transforming the second proportional voltage toa discharging current signal; wherein the discharging current signaldischarged the energy storage device when the power switch duringoff-time period, and the energy storage device produces the voltagelimited signal, which is proportional to output voltage of the secondarywinding of the power converter, to control the power switch.
 21. Thecircuit of claim 20, wherein the second transforming circuit comprises:a second voltage-current converter, transforming the second proportionalvoltage to a second current; and a second current mirror circuit,mirroring the second current to a discharging current signal beforedischarging the energy storage device.
 22. The circuit of claim 20,wherein the voltage limited signal of energy storage device when thepower switch during off-time period is according to following equation:$V_{L\text{-}{off}} = {y \times \frac{V_{O} \times B}{C} \times \frac{T_{off}}{R_{y}} \times N_{x}}$wherein y is current mirror transfer ratio; C is capacitance of theenergy storage device; V_(O) is an output voltage of the powerconverter; B is the proportion of the second proportional voltage;T_(off) is time of the power switch during off-time period; Nx is aturns ratio of the auxiliary winding and the secondary winding; andR_(y) is a voltage to current conversion ration.
 23. A output regulationcircuit of a power converter, the power converter including a primarywinding, a secondary winding, an auxiliary winding and a power switch,comprising: a second transforming circuit, receiving a secondproportional voltage from the auxiliary winding of the power converter,and transforming the second proportional voltage to a dischargingcurrent signal; an energy storage device, discharged by the dischargedcurrent signal when the power switch during off-time period; and whereinthe energy storage device produces a voltage limited signal, which isproportional to an output voltage of the secondary winding of the powerconverter, to control the power switch of the power converter.
 24. Thecircuit of claim 23, wherein the second transforming circuit comprises:a second voltage-current converter, transforming the second proportionalvoltage to a second current; and a second current mirror circuit,mirroring the second current to a discharging current signal beforedischarging the energy storage device.
 25. The circuit of claim 23,wherein the voltage limited signal of energy storage device when thepower switch during off-time period is according to following equation:$V_{L\text{-}{off}} = {y \times \frac{V_{O} \times B}{C} \times \frac{T_{off}}{R_{y}} \times N_{x}}$wherein y is current mirror transfer ratio; C is capacitance of theenergy storage device; V_(O) is an output voltage of the powerconverter; B is the proportion of the second proportional voltage;T_(off) is time of the power switch during off-time period; Nx is aturns ratio of the auxiliary winding and the secondary winding; andR_(y) is a voltage to current conversion ration.
 26. The circuit ofclaim 23, wherein the energy storage device is an electric capacity. 27.The circuit of claim 23, wherein the energy storage device is aninductance.